Yoshitada Watanabe

Sliding contact characteristics between self-lubricating composite materials and copper

Simultaneous measurements of contact electric resistance and coefficients of friction on three types of composite materials containing laminar solid lubricants were conducted. Contact resistances of new composite materials (CM-4, CM-5) were as low as 1/10, compared to those of a previously prepared composite material (CM-1) in the range of the measurement conditions (50-1000 gf, 0.1-10 A). Coefficients of friction for the new materials were slightly higher because of the reduction of the contents of solid lubricants by the additions of Cu, Sn, and Ag for lowering the resistivities. It was concluded that these new composite materials were sufficiently beneficial for use in sliding electric contacts. The current-voltage characteristics indicated that the occurrence of fritting phenomena observed on the composite material CM-1 was not observed on CM-4 and CM-5, because the generation of Joules heat was suppressed by the effective functioning of solid lubricants with the resistance of CM-4 and CM-5 lower than that of CM-1.<<ETX>>

An investigation for the method of lifetime prediction of Ag-Ni contacts for electromagnetic contactor

Electrical contacts are widely used for telecommunication and electric power systems as a device mechanically making and breaking electrical current. In the future, they will be more indispensable. In this paper, we explored the possibilities of early lifetime prediction of Ag-Ni contacts for an electromagnetic contactor. Contact erosion often leads to the contact failure and the system fault. Especially, for heavy electrical systems, the failure can cause critical troubles. We must estimate approximate periods of the system fault to avoid the troubles. The tests of lifetime are very important for that purpose. However, the tests often require an enormous amount of time. We investigate the possibilities of lifetime prediction of contacts. In the past work, we confirmed that the mass loss could lead to the contact failure of Ag-Ni contacts and the mass loss of cathode was in proportion to total arc energy generated between the anode and the cathode. At this time we measured the mass losses of cathodes with a few making and breaking operations for more samples, and accurately predicted the mass losses after a lot of operations. We compared them with experimented results of a lot of operations.

Sliding contact characteristics between composite materials containing layered solid lubricants and carbon

Abstract Metallic composite materials containing solid lubricants such as MoS 2 and WS 2 are frequently applied as sliding electrical contacts. However, few reports have been presented describing details of the electrical characteristics of such materials. Sliding contacts were made between such composite materials and carbon, and the electrical contact resistances and coefficients of friction were measured while changing loads and currents. The results obtained were examined. Although contact resistances tended to decrease with increasing d.c. electric current from 1 to 10 A, the coefficient of friction μ remained stable at around 0.1. It was therefore found that further improvements in smoothness of motion could be attained by using carbon ( μ = 0.1) as the mating material rather than using copper ( μ = 0.3) for the purpose when applying this composite material as sliding electrical contacts.

An evaluation method of the contact erosion based on the DC mode test of electromagnetic contactor

Electrical contacts are widely used for telecommunication and electric power systems as a device mechanically making and breaking electrical current. In the future, they can be still indispensable. Furthermore, the performance and reliability of electrical contacts must be more improved. Details of the mechanisms, however, have not completely been revealed yet, so that contact erosion and material transfer sometimes lead them to contact failure. We focus on two issues about contact erosion. In these years, volumetric method was proposed as the new evaluation method of surface erosion. However, few papers compare it with weighing method of measuring the mass change in detail. Hence, we investigated relationship between the number of switching operations and the amount of wear in electromagnetic contactor, and compared two methods. Furthermore, electromagnetic contactor is often used in the systems with an AC power supply. On the other hand, the DC mode test provides more fundamental data for us to investigate the electrical contacts than the AC mode test. We compared the data of the DC mode test with that of the AP mode test and described the possibility to estimate contact erosion with an AC power supply in terms of the DC mode test. The result of the DC mode agreed well with that of the AP mode in the case of low load current and a small operation number. We could also show an availability of volumetric method in early lifetime prediction.

New instrument for measuring contact resistance developed for studying electrical contact phenomena

Abstract A new experimental apparatus for measuring the electrical contact resistance is described. This apparatus is essentially a conventional balance, modified for the examination of electrical contact resistance changes of silver and some other metal specimens due to increases and decreases in load and current. The results obtained show that plastic deformation takes place at the contact spots in response to an initial increase in load and elastic deformation occurs on a subsequent decrease in load. When a pair of Nichrome rods, which have a much higher resistivity than the silver specimen, are brought into contact with each other, the areas of the contact spots appear to be larger than those calculated. A fritting phenomenon, first studied in detail by Holm, occurred on the contact surfaces of the rods when they were subjected to heat and oxidation in the course of the experiment.

Low-Speed Sliding Test on New Cu-Sn-Based Composite Materials

The author prepared new composition of Cu-Sn based composite materials containing lamellar solid lubricants, and measured their performance with focus on contact resistance and the coefficient of friction using a low-speed tribometer. Among three kinds of composite materials, the composite material containing 26wt.% of total solid lubricants was lower in both of contact resistance and the coefficient of friction and showed stable characteristics compared with those containing 25wt.% and 35wt.% respectively. The author analyzed the characteristics of these materials using several techniques including BSE image, element analysis through EPMA, and mapping analysis, and examined why the composite material containing 26wt.% of total solid lubricants showed higher performance.

Low-speed sliding test characteristic of sliding contact containing solid lubricants for use under severe application conditions

Development of a new sliding contact, usable under severe conditions such as high temperature, extremely low temperature or high vacuum, has recently become an urgent necessity. This research mainly examines the contact resistance and coefficient of friction of three kinds of self-lubricating composite materials with electrical conductivity and mechanical stiffness. The result showed that a composite material (CMML-1) containing the lowest quantity of solid lubricants (WS/sub 2/, graphite) was low in both contact resistance and coefficient of friction and lower in fluctuation. By EPMA analysis, the Sn contribution to electrical conductivity was suggested.

Low Speed Sliding Characteristics of Cu-Fe-W-Based Composite Material Contacts Containing WS2

Recently, Sliding electrical contacts are used in severe operating conditions, such as high temperatures, very low temperatures and ultra-high vaccums. They also require high reliability. In this research, three kinds of composite materials, containing different elements, make use of WS2 show excellent characteristics in the atmospheres mentioned above. A Cu disk was examined as a partner materials. Consequently, it becomes clear that composite materials containing the smallest quantity (30 wt.%) have excellent characteristics in contact resistance and coefficient of friction.

Sliding Scar Analyses of High Speed Sliding Contact Characteristics of Cu-Sn Based Composite Materials Containing WS2

Three types of composite materials containing lamella solid lubricants, such as WS2,C, etc. in the ratio of 40, 50, and 60 (vol.%) respectively were subject to the sliding test at relatively high-speed 1000 (min-1), (1.0(m/s) ) to measure their contact resistance and coefficient of friction simultaneously. The result showed that, with increasing content of solid lubricants by 10 (vol.%), the contact resistance increased by 100 (mΩ) at the highest and the coefficient of friction decreased by about 0.1. Review was made by AFM sliding scar analysis on what kind of influence the solid lubricant and conductive materials, namely, the components of composite materials or factors causing the above results, exert on the contact surface condition.

A Study on Contact Spots of Earthquake Disaster Prevention Relays

This paper reports on the effect of switching action on the contact surfaces of earthquake disaster prevention relays. Large-scale earthquakes occur frequently in Japan and bring extensive damage with them, and fire caused by electrical equipments is one example of the serious damage which can occur. Earthquake sensors capable of maintaining a high level of reliability when earthquakes occur play an important role as a means of minimizing this damage. For this reason, we carried out observations by focusing on samples which had either been subjected to an electric current of 10mA or 0.1 A. The samples of 10mA exhibited low and constant contact resistance despite the addition of seismic motion, while the samples of 0.1 A samples exhibited varying contact resistance and damage on their contact spots resulting from the addition of seismic motion. The sample surfaces were then observed using an atomic force microscope (AFM) in tapping mode and a surface potential microscope (SPoM). As a result, we found that even the unused earthquake disaster prevention relay (standard sample) which had a surface lined with asperities on its parallel striations formed by irregular protrusions due to dust and other deposits. In addition, scanning the contact surface with the SPoM at the same potential revealed the occurrence of differences in surface potential which varied in response to the asperities on the striations.